Abstract: A direct-current electromagnetic device for nondestructively detecting localized discontinuities in ferromagnetic objects is disclosed. The device comprises an adjustable dc excitor means, a magnetic flux injector means, an external magnetic field detector means, a plurality of position sensors, a signal processing means and a control means. It is particularly adapted for detecting flaws in soiled and distorted ferromagnetic objects such as water wall tubes in industrial boilers. An apparatus incorporating the device and a method of detecting discontinuities are also disclosed.

Abstract: A static inverter is provided suitable for use as a high frequency power supply utilizing sets of switching thyristors which are switched in pairs in a predetermined sequence, with series-related capacitors, and which includes diodes connected to insure turn-off of the thyristors and to limit the maximum voltage that can occur across the sets of thyristors.